Myocardial infarcts heal by scarring because cardiocytes cannot replicate after injury, and because there are no muscle stem cells in the heart. Previous studies showed that MyoD gene transfer or skeletal myoblast grafting can form new contractile tissue in injured hearts, but that skeletal muscle does not form electromechanical junctions with surrounding myocardium. The goals of this project are 1) to develop strategies to repair infarcts with muscle that integrates electrically and mechanically with the remaining myocardium; and 2) to understand how cardiac wound healing is normally regulated to permit rational design of therapies to enhance infarct repair. Specific Aim 1 will determine whether cardiac myocytes from developing or adult hearts can be grafted into injured adult hearts. Physiological studies will determine if cardiocyte grafting improves regional contractile function in vivo. In Specific Aim 2, skeletal myoblasts will be genetically modified to express N-cadherin and connexin 43, the principal proteins of cardiac adherens and gap junctions, respectively. Co-cultures of cardiocytes and transfected skeletal muscle will be studied structurally and functionally for adherens and gap junction. In vivo studies will determine if the genetically modified cells integrate into host myocardium and restore regional contractile function after injury. Specific Aim 3 focuses on the role of osteopontin, a matrix adhesive protein highly expressed by macrophages, in cardiac wound repair. We will administer anti-osteopontin antibodies to rats with cardiac injury and also study cardiac repair in osteopontin- deficient mice. Cell culture studies will determine if osteopontin promotes phagocytosis by macrophages or adhesion and migration of cardiac fibroblasts. In Specific Aim 4 we will study the time course of growth factor (bFGF, VEGF, PDGF, TGF-beta) production following cardiac injury to identify candidate mitogens. Individual growth factors will be studied by administering recombinant molecules systematically and through the use of blocking antibodies in rats with healing infarcts.